1. Field of the Invention
The present invention relates to a novel halogenating agent, preparation process and use of the agent.
2. Related Art of the Invention
Many processes have been conventionally known related to the halogenating reaction of organic compounds. Halogenating agents which can be generally used are hydrogen halogenide, halogen-phosphorus compounds, halogen-sulfur compounds and halogen simple substances. However, these substances have high corrosivity and toxicity, and many of them require specific equipment and technique for handling these agents. Consequently, in view of ease handling, safety and reactivity, development research on various halogenating agents has been continued still now. Particularly in the preparation of fluorine compounds, fluorinating agents are generally very dangerous. Thus, specific equipment and techniques having a further high level as compared with other halogenating reaction are required and also lead to higher load in economy.
Fluorinating agents which have been conventionally used for a fluorinating reaction are fluorine, hydrogen fluoride, and tetrafluorinated sulfur. However, these conventional fluorinating agents are difficult to handle due to toxicity, corrosivity and danger of explosion in the reaction step and require specific equipment and techniques. Further, poor selectivity of a fluorine bonding in the reaction is also a problem. On the other hand, development of new products utilizing fluorine compounds has been carried out in functional materials, physiologically active substances and other various fields. In recent years, various fluorinating agents have been developed to cope with these demands.
For example, as a representative agent which has been developed for a fluorinating agent of a hydroxyl group, carboxyl group and other oxygen containing functional groups, U.S. Pat. No. 3,976,691 has disclosed DAST (diethylaminosulfurtrifluoride). DAST has been introduced as an excellent fluorinating agent of oxygen in an alcoholic hydroxyl group or a carbonyl group. However, in the preparation of DAST, highly dangerous tetrafluorinated sulfur is reacted with dimethylaminotrimethyl silane at a low temperature of -78.degree. C. to -60.degree. C. Thus, a specific manufacturing facility is required. As to safety, explosion has been reported on the production and use of DAST [J. Fluorine Chem., 42 137 (1989)].
Further, WO 96/04297 has described that tetraalkyl-fluoroform-amidinium=salt is an excellent fluorinating agent of a carboxyl group. However, no description has been found on the fluorinating reaction of other functional groups. The application has described that halogen ions are included as a counter ion of tetraalkyl-fluoroformamidinium salt. However, in practice, PF.sub.6.sup.- is an only one example shown as a counter ion. Therefore, the present inventors have prepared 1,3-dimethyl-2-fluoroimidazolinium=hexafluorophosphate in accordance with the process of WO 96/04297, and used for the replacement of individual hydroxyl group on benzoic acid, benzyl alcohol and n-octanol into fluorine. As a result, benzoyl fluoride has been formed from benzoic acid. However, formation of fluorine compounds could not be observed in the fluorinating reaction of benzyl alcohol and n-octanol. Japanese Laid-Open Patent HEI 4-308538 has disclosed a halogenating reaction of primary alcohol by using a haloiminium salt as a halogenating agent. Japanese Laid-Open Patent HEI 9-67299 has described a halogenation reaction of carboxylic acid. Both literatures have described that the counter ion of haloiminium salt includes a halogen ion. However, in practice, the counter ion is an example of Cl.sup.- alone. Quite no description is found on a fluorinating agent in particular.
Further, DE 2627986 and Japanese Laid-Open Patent SHO 52-156810 have described use of bis-dialkylaminodifluoromethane as a reaction catalyst in the preparation of perfluoroalkoxypropionyl fluoride. However, no description has been found on a fluorinating agent. The preparation is carried out by reacting hexafluoropropene oxide with tetraalkylurea, and the source of fluorine is expensive and difficult to handle.
As a mentioned above, the fluorinating agent of an oxygen containing functional group has not yet satisfactorily developed for use in industry in view of preparation process, selectivity, yield and economy.